Bench Testing a Valeo Alternator

[glassescase]

I am having problems bench testing an alternator. It is a 2 pin 3 wire alternator, I think its called 3 wire

I have the B post of the alternator connected to the positive of a battery. The chassis of the alternator is connected to the negative of the battery.
If I test from the B post to what I think is the L pin I get 12 volts. From YouTube videos, if I connect a light bulb from the B post to the L pin, it should light up.
It doesn't. I fitted a new slip ring, if I have this reversed, top ring goes to wire A instead of B and bottom ring goes to B instead of A what problems would this cause?

Any idea why, even though I have 12v the bulb which is only 2.3 watt it wont light? The bulb does work


thanks glassescase

[Peter-jforf]

From EX Auto sparks now retired 83 years....depends on type of Alternator your testing....older alternators with internal regulators...yes your correct in warning light to live Pos + post....the other wire on test bulb to " L ".....but much older Alternators used external regulator....and they need a " pos + to the Field terminal...and a negative to excite the field....the then 3rd terminal...sends a output to the regulator ....which in turn now regulates the out-put and controls a warning lamp........these were much used in the 60s / 70s / 80s......then all had internal Regs.....now we come up to these cars now fitted with....not ECUs running running engine etc etc etc....but one main power pos +....a small terminal which transmits RPM pulse to what is called the "Main body control unit ".....this is much advanced and does ..".Well everything " in the running of the vehicle..all warning lights etc etc etc....all in the last 2/3 years have "Power control units ", best i can help without knowing more re - alternator / car you have..........Peter

[glassescase]

Cheers Peter,
my voltage regulator sits on the outside of the alternator and is bolted to it. The socket for the cars wiring harness only has 2 pins, my car is 2005 Rover 75 CDT, diesel.
I dont know why but last night I removed the new voltage regulator and refitted the original and hay presto the light works.

None of us could have known it was faulty but now if anyone has the same problem, I and anyone reading this thread, can be quick to suggest a faulty voltage regulator. I will spin the alternator up with a second bulb connected to see if the first bulb goes out and the second bulb lights.
Waste of money on the regulator, it has been on my bench for about 3 years, £9.60 for a slip ring, £9.60 for a bearing puller and £6.50 for some J.B weld and for a tad over £25 I have a working alternator......hopefully.


Once you know how to repair, it is easy.

glassescase